Single surface grills are widely used in commercial food service establishments for cooking a wide variety of food products. Some food products such as hamburger patties require cooking on both sides and, in single surface grills, it is necessary for the operator to turn the patties after they have been cooked on one side for cooking on the second side. This increases the overall cooking time and the amount of operator attention required for cooking such food products. In addition, some food products such as hamburger patties tend to shrivel and curl during one-sided cooking, unless a restraining pressure is applied to the upper side of the food product. When the food product shrivels or curls during cooking, the contact area between the food product and the cooking surface is reduced and this adversely affects uniformity of cooking of the food product and the appearance of the cooked food product.
Cooking apparatus have heretofore been made with upper and lower cooking platens for two-sided cooking of food products such as hamburger patties. Two-sided cooking apparatus generally reduce the overall cooking time and amount of operator attention required for cooking the hamburger patties. However, there are a number of interrelated problems encountered in two-sided cooking apparatus that are not encountered in single surface grills.
The upper cooking platen in two-sided cooking apparatus for commercial food service establishments are generally large enough to enable cooking of a number of individual hamburger patties at the same time. The hamburger patties are preformed in several different nominal sizes and thicknesses and are commonly frozen for storage and transportation. The frozen patties are relatively rigid when initially placed on the lower cooking platen and if the upper platen rests only on the thickest patty or patties, even small differences in the thickness of the patties in the group being cooked could delay good heat transmitting contact between the upper platen and some of the thinner patties and result in uneven cooking of the patties. On the other hand, the patties soften and shrink or decrease in thickness as they thaw and cook. The weight of the upper cooking platen, if unrestrained or controlled, is such that it could excessively compress or compact the hamburger patties and adversely affect the texture and appearance of the cooked patties. Thus, two-sided cooking apparatus present several special problems including accommodating variations in initial thickness of the individual patties in the group being cooked; accommodating the decrease in thickness of the patties that occurs during cooking; preventing excessive compaction of the patties; and accommodating different groups of patties of nominally different thickness. In addition, in two-sided cooking apparatus, there is the problem of moving the upper platen at the beginning and end of the cooking cycle. In order to facilitate timed cooking, the two-sided cooking apparatus is desirably arranged to automatically raise the upper platen at the end of a cooking cycle to stop cooking by the upper platen and enable removal of the cooked products from the lower platen.
U.S. Pat. No. 4,444,074 discloses a conveyor type two-sided cooking apparatus in which the upper platen is power operated to a raised position. A conveyor advances a group of hamburger patties onto the lower platen and stops and the upper cooking platen is then allowed to drop by gravity onto the upper side of the group of patties on the lower platen. Platen stops are provided to control the minimum spacing of the upper platen relative to the lower platen during cooking, to prevent excessive compaction of the cooked patties. After the patties are cooked on both sides, the upper platen is power operated back to its raised position generally paralleling the lower platen and the conveyor is then operated to move the cooked patties off the lower cooking platen. Such conveyor type two-sided cooking apparatus are special purpose machines usable only for cooking certain food products such as hamburger patties that can be advanced by a conveyor onto and off from the lower cooking platen and they are not adapted to alternative use as a single surface grill.
Various clamshell type two-sided cooking apparatus have also been made in which the upper cooking platen is mounted on a platen support arm for swinging movement about a horizontal axis between a lower cook position and a raised position, and automatically raised at the end of a timed cooking cycle. Some prior art clamshell grills such as disclosed in U.S. Pat. Nos. 2,009791; 4,008,067 and 4,165,682 used counterbalance means to assist raising of the upper platen and in U.S. Pat. No. 4,483,239 the upper platen is power operated to a raised position by a pneumatic cylinder at the end of a timed cooking cycle. In some prior clamshell grills, the upper platen is pivotally mounted on the platen support arm for tilting movement about a horizontal axis relative to the platen support arm to rest the upper surface of the food products. In U.S. Pat. Nos. 2,632,379 and 4,483,239, the upper platen is rigid with the platen support arm and spacing of the upper platen relative to the lower platen during cooking is effected by vertically adjusting the pivot at the rear of the platen support arm and adjusting an arm stop at the distal end of the platen support arm. Clamshell grills have also been made with a plurality of upper platen stop pins adjustably mounted on the upper platen and extending downwardly through the cooking face of the upper platen for engagement with the upper face of the lower platen to control the space therebetween. However, the stop pins limited the usable cooking area on the upper and lower platens and made it difficult to clean the upper platen. Further, the stop pins were in the cooking area and heated by direct contact with the cooking platens, and grease and other debris normally created by cooking hamburgers and the like tended to bake on the stop pins and impede their adjustment.